Mobile app works differently on different devices

I'm developing a mobile app that is having several differences according to the device it is working on.

In the emulator everything seems ok, but when installed on a Samsung (Android OS) almost nothing works, and on another Android device most functionalities work (same thing with an iPhone). Also, it is barely impossible to debug the app on the Samsung device, what makes everything even worse.

Does anyone has any idea of what causes these compatibility/rendering issues and how to solve them?